A typical conventional phased-array antenna has an arrangement of radiating elements where the relative phase of radio frequency (RF) waves propagated through each radiating element can be controlled to steer the "beam" of the antenna's radiation pattern. In one type of phased-array antenna, known as active arrays, each radiating element has associated electronics that include amplifiers and phase shifters. The distributed nature of the active array architecture offers advantages in, for example, power management, reliability, system performance and signal reception and/or transmission. However, the electronics associated with the radiating elements typically cause an active array antenna to be much thicker than a passive array antenna. In some applications, such as, for example, airborne externally mounted arrays, the thick antennas are impractical.
One example of an active array is disclosed in U.S. Pat. No. 5,276,455 (hereinafter "the '455 patent") issued to Fitzsimmons, et al., Jan. 4, 1994, assigned to the same assignee as the present invention and incorporated herein by reference in its entirety. FIG. 7 of the '455 patent, reproduced in the drawings of this application as FIG. 1, is an exploded view of an active array antenna 100 disclosed in the '455 patent for use in receiving or transmitting circularly polarized RF signals. Antenna 100 has an antenna honeycomb 132, a module honeycomb 128 and a feed honeycomb 134, each having a plurality of waveguides aligned with a corresponding waveguide in the other honeycombs. Each waveguide of honeycomb 132 contains a dielectric 146 and separate polarizer 148. Each waveguide of honeycomb 128 contains an "in-line" active array module 130 (i.e., the substrate of each module 130 is parallel or "in-line" with the direction of the received or transmitted RF signal propagation), and each waveguide of honeycomb 134 contains a dielectric 146.
Further, antenna 100 has a waveguide feed network 112 for propagating RF signals to or from feed honeycomb 134, and multilayer wiring boards 140a and 140b for distributing power and logic signals to modules 130. Multilayer wiring boards 140a and 140b do not propagate the RF signals transmitted or received by antenna 100. Rather, modules 130 perform waveguide-to-waveguide transmission of the received and transmitted RF signals via antenna honeycomb 132 and feed honeycomb 134.
Compared to other existing phased-array architectures, the phased-array of the '455 patent offers improvements in size, thickness, cost, maintainability, reliability, testability, and assembly. But, of course, improvements are generally always desirable. Antenna 100 is still relatively thick because of honeycombs 128, 132 and 134 and the "in-line" configuration of modules 130 and separate polarizers 148. Further, because moisture in hollow waveguide may detrimentally affect the antenna's performance, arrays that employ hollow waveguides generally require pressurization with a dry gas to reduce moisture build up, thereby increasing complexity of the antenna.
In addition, modules 130 have extension substrates for input and output couplers for inputting and outputting RF signals to or from antenna honeycomb 132 and feed honeycomb 134, as well as a carrier substrate for supporting and interconnecting monolithic microwave integrated circuits (MMICs) for amplifying and phase shifting the received or transmitted RF signals. The extension substrates are bonded to the carrier substrate, which are then covered and sealed. The complexity, assembly and yield cost cause such modules 130 to be relatively expensive to fabricate. Even though the individual cost of each electronic module 130 is modest, the large number of modules required to assemble an array represents the largest antenna cost component.